Specifically "dictatorship of the proletariat", which was basically an 1800s gothic way to say "direct democracy for workers". Marx is somewhat infamous for the way he makes his ideas sound scarier than they are

And to clarify, most revolutions fail or adopt bureaucracy primarily to defend themselves from outside, capitalist influence, power corruption probably plays a part too but state power used by socialists is actually part of the plot

The vast majority of (Let's use Vietnam as an example) is proletariat. So the vast majority of people are dictating terms to a small subset with different class interests. It's nothing like the dictatorship in, let's say the Netherlands, where a small group of capitalists dictate terms to the large body of proletariat, and the bourgeois political apparatus mediates in favour of bourgeoisie class interests. There's no corruption taking place, just the necessities of market economics.

This dictatorship will naturally "dissolve" when there are no more other classes (bourgeoisie et all) to oppress, since it will no longer serve the proletariat's interests.